Thought Leadership Article – “Breaking the Cabin Barrier” from Warwick Acoustics

Ian Hubbbard, CCO, Warwick Acoustics

We all understand and appreciate great music, especially when it is reproduced well, and a significant time listening to music takes place in the unique private environment of our car.

Hence, more than half the cars on the market have a “premium” car audio system and, audio companies invest heavily in technology that attempts to reproduce music ‘as the artist intended’ or ‘feeling the performance as if you were there’ by making the audio sound bigger than the car.

The philosophy is to reproduce the music as if you were listening and experiencing it in the environment the music was produced. We know a musician, band or orchestra was not in a car when they recorded their music. Typically, they would be in a small recording studio approx. 20-30m² in size, perhaps 70m²for a rock band, and in some cases, like an orchestra, in a concert hall several thousand m².

The interior of a typical premium car is in the region of 7m². The environment the music is recorded in makes a huge difference to the ambience of the music we experience, and it is this ambience that audio engineers are aiming to reproduce in our car cabin when designing an audio system.

Before digging deeper into the ‘how’ - for full disclosure, on top of my 20+ years of delivering premium audio solutions to the automotive industry whilst heading up Sony’s global automotive business, I currently lead the commercialisation of Warwick Acoustics Ltd’s automotive business. One of my motivations for joining Warwick Acoustics was due to their revolutionary technology having some unique advantages over conventional loudspeakers, which opens up opportunities for audio designers and car manufacturers wanting to make the audio reproduction sound bigger than the car itself. In short, I saw an opportunity to fundamentally make the experience “bigger than the physical limitations of the car”.

Car audio designers today use clever speaker placement and digital signal processing (DSP) to make the audio sound bigger than the car, creating a wide, deep and immersive soundstage and recreating the original ambience.

This is where it gets a little techy, but bear with me…

Speaker Placement & Packaging

Let’s begin with speaker placement, assuming we have a basic audio system with speakers in the front and rear doors of the car already. We are talking about how to make an audio system sound bigger.

Traditionally, speakers are packaged in the car where space is available, this typically leads to sub-optimal placement for creating sound. An example of this is speakers down low in the front doors, a good place for packaging, but there is no acoustic benefit to audio directed at your ankles.

By contrast, electrostatic speakers are just a millimetre or so thick and when packaged, take no more than 10mm of depth, allowing them to be placed in acoustically optimal locations whilst ensuring that the interior design language of a car is uncompromised. This means broad audio spectrum speakers in the headlining, A-pillars, dash top or headrests are easily achievable.

Digital Signal Processing (DSP)

Having packaged the speakers, DSP is applied and enables the magic to happen by allowing audio designers to adjust and add:

Time alignment: Adjusts when sound reaches your ears from different speakers, making it seem like it's coming from beyond the dashboard or windshield.

Phase manipulation: Carefully controls phase relationships between channels to create the illusion of width and height.

Upmixing algorithms (like Dolby Atmos & Sony 360 Reality Audio): Convert stereo into 3D surround, placing instruments or effects in a 360° sound field. Atmos and other up-mixers use a technique called object-based audio that enable “sound objects” to be placed in a 3D space independent of both number of speakers and their location inside the cabin. You perceive sound as moving around you and is used to bring movies to life.

This is all very clever, and if you have been to the cinema in the last 10 years or so, you are likely to have experienced this. But, it’s difficult to get right in a 7m² car cabin, and if not flawlessly implemented, it can sound artificial.

The goal is sound that appears to come from “beyond” the physical speaker positions.

Ambience

Ambience is closely associated with immersion, as in ‘immersive audio’, all of which is managed by the DSP outlined above. But let me break down some of the characteristics of the sound that is being manipulated and simulated by the DSP.

Simulated early reflections and late reverberations help to mimic large concert halls or clubs. Making reverb tails or echoes continue slightly longer than physically possible inside a car expands the perceived space.

Head-Related Transfer Functions are used to shape how sounds are filtered based on ear shape and position, fooling your brain into thinking sound is coming from outside the cabin.

Other techniques, generically referred to as psychoacoustics, are used to manipulate sound interpreted by the brain.

Subtle EQ shaping mimics the tonal shifts of sound coming from a distance (e.g. roll-off of highs, soft reverb).

Humans are particularly good at hearing acoustic reflections thanks to the fact that we have two ears spaced apart. After we interpret the location and size of the sound, we then naturally listen for further evidence of that sound which allows us to determine the surrounding space of our environment.

Time and Space

A long time ago, our early ancestors relied on their hearing to detect the location and size of the source of sound to determine if a sound represented a threat or their next meal!

As soundwaves travel through the air, they have a tendency to flatten and spread out, much like the ripples from dropping a pebble into a flat smooth pond. The water waves begin tall and narrow and end up low and spread out.

Even if you had not seen the pebble entering the water, you would be able to tell from which direction it had entered the water. In the same way you can tell from where a sound has come from and get a sense of how far away the sound was when it was produced.

Conventional loudspeakers due to their conical shape, produce sound waves that begin much like where the pebble entered the water and disperse through the air before reaching our ears. Which means in our car cabin where speakers are no more than 1 to 3 m away from our ears, they haven’t been able to travel very far and hence the sound is perceived as being close to our ears.

The joy of listening to sound produced from an electrostatic loudspeaker is that it starts off appearing to be flat and we humans perceive this as a sound that has begun further away from our ears and bigger than the car.

A welcome by-product of all this game-changing performance from electrostatic loudspeakers means the DSP doesn’t have to work so hard when simulating immersive audio characteristics. This frees up processing power for other functions within the vehicle or allows for less power-hungry DSPs.

The Bottom Line

We want to make car audio systems sound bigger than the car to make us feel like we are listening to the music in the environment it was originally produced. Imagine an in-car experience that allows you to feel the atmosphere and acoustics of the Sydney Opera House, Ronnie Scott’s Jazz Club in London or Electric Lady Studios in New York.

There are many techniques for artificially re-creating sound that gives us this illusion of space, but the closer we can mimic the reproduction of sound that our brain is expecting through the use of electrostatic loudspeakers, the more natural the recreation of the sound will feel and …. the cabin barrier will be broken.